re = /\S+\s\d+\/\d+\/\d+/m
str = 'Buxtehude /1234 KundenAuftragEinsatzart1 698874/6387/01
KundenAuftragEinsatzart 698874/6387
Musterstadt /1234 KundenAuftragEinsatzart2 698874/6387/01
KundenAuftragEinsatzart3 698874/6387/01
KundenAuftragEinsatzart4 698874/6387/01'
subst = ''
result = str.gsub(re, subst)
# Print the result of the substitution
puts result
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for Ruby, please visit: http://ruby-doc.org/core-2.2.0/Regexp.html